Field
The present invention generally relates to wireless power transfer.
Description of the Related Art
Recently, there has been known a wireless power transfer system including a power transmission device which wirelessly (non-contact) transmits power without being connected by a connector and a power receiving device which receives power supplied from the power transmission device (“Wireless technology developed to transmit power lights up a 60 W bulb in tests”, Nikkei Electronics, Vol. 966, Dec. 3, 2007).
Through the wireless power transfer, a power receiving device can be charged by a simple operation of placing the power receiving device on the power transmission device. However, the power receiving device may not be able to be charged even though a user has placed the power receiving device on the power transmission device when the power transmission is not available due to some error. Therefore, it is necessary to notify a user of a state of the wireless power transfer. Japanese Patent Application Laid-Open No. 2013-27074 discloses a technique of notifying a user that the power transmission device having a plurality of power transmission coils has recognized the power receiving device, that the power receiving device is normally supplied with power, and which one of the coils is supplied with power during power transmission. Japanese Patent Application Laid-Open No. 2012-100491 discloses a technique in which the power receiving device notifies a user that a charging period of when the power transmission device transmits power to a plurality of power receiving devices becomes longer than that of when the power transmission device transmits power to a single power receiving device.
As described in Japanese Patent Application Laid-Open No. 2012-100491, in the wireless power transfer system in which the power transmission device can transmit power to the plurality of power receiving devices, the number or the power of the power receiving devices to which power can be transmitted may be limited depending on the capacity of the power transmission device. A case will be considered where the user places another power receiving device, different from the plurality of power receiving devices, on the power transmission device which is transmitting power to the maximum number of power receiving devices to which the power can be transmitted. In this case, the power transmission device may not be able to allocate the power to be transmitted to the another power receiving device, and the another power receiving device is not appropriately charged even though the another power receiving device is placed on the power transmission device.
However, in the related art, the user cannot recognize the power transmission device which cannot appropriately transmit power to the another power receiving device placed additionally. For example, the power transmission device in this case is transmitting power to the maximum number of power receiving devices to which the power can be transmitted.
Japanese Patent Application Laid-Open Nos. 2013-27074 and 2012-100491 notify that the power transmission device has recognized the power receiving device and that the charging period becomes late. However, Japanese Patent Application Laid-Open Nos. 2013-27074 and 2012-100491 do not consider allowing the user to recognize the power transmission device which cannot appropriately transmit power to the another power receiving device additionally placed before the user places the another power receiving device on the power transmission device.